The present invention relates to an enantioselective process for preparing optically pure β-cycloalkenyl-substituted alanines (Formula I, IA and IB), which could be easily converted to cyclic amino acids (Formula II) that are key intermediates for the ACE inhibitors ramipril (Formula III) and perindolpril (Formula IV).

Ramipril [A. Kleemann, J. Engel, Pharmaceutical Substances, 4th Edition, page 1785, Thieme Verlag Stuttgart, 2001] and perindolpril [EP 1565485, EP1688427] are ACE inhibitors which are frequently employed in the medical management of hypertension. One of the key intermediates is the cyclic amino acid of Formula II (n=1, 2). The five member ring amino acid with Formula II, wherein n is 1, is used for the preparation of Ramipril [WO 2009/098251, US 2009/0017509, WO 2007/079871]; while the six member ring amino acid with Formula II, wherein n is 2, is used for the preparation of perindolpril [EP 1354876, US 2007021490, WO 2004083237, WO2007085933].
The prior art for preparing the above mentioned amino acids employed such processes as chemical resolution [e.x. DE 3345355, EP 115345] or bio-transformation [e.x. US 2009/0017509]. However, these processes waste about half of the quantity of the precursor material and produce undesired isomers.